| This page incorporated content from Jastrow_illusion,
a page hosted on Wikipedia. Please consult the history of the original page to see a list of its authors. Therefor, this article is also available under the Creative Commons Attribution-ShareAlike License
The optical illusion is credited to Professor Joseph Jastrow, a pioneering psychologist, in 1891.
It's sold as part of many magic kits to children.
Variations of the shape